Genital HIV-1 viral load is a major predictor of sexual and perinatal HIV transmission, and strategies to decrease HIV-1 shedding while promoting vaginal health are urgently needed. We hypothesize that hydrogen peroxide-producing Lactobacillus (L. crispatus and L. jensenii), key components of the normal vaginal flora, decrease genital HIV-1 RNA and DNA shedding among HIV-1-infected women by direct viral inhibition and also by relative suppression of potentially pathogenic vaginal bacteria associated with bacterial vaginosis (BV). We propose to evaluate this hypothesis using archived cervicovaginal lavage (CVL) and cervical cytobrush samples from parallel cohorts of HIV-1-infected women in the United States and Kenya. Specifically, we will: 1. Examine the effect over time of L. crispatus, L. jensenii and L. iners presence and concentrations on HIV-1 RNA load in CVL, as well as the effect of these organisms on pro-inflammatory cytokines and other BV-associated flora. We anticipate that acquisition and/or higher concentrations of L. crispatus and L. jensenii (but not L. iners) will result in a significant decrease in CVL HIV-1 RNA, accounting for other factors such as plasma viral load and antiretroviral therapy, and that this protective effect may be mediated by down-regulation of pro-inflammatory cytokines and/or suppression of BV-associated bacteria. 2. Assess the longitudinal effect of vaginal Lactobacillus species, other BV-associated organisms, and pro-inflammatory cytokines on endocervical HIV-1 DNA quantitation, as well as endocervical HIV-1 RNA. We hypothesize that the protective effect of L crispatus and L jensenii will extend to the endocervix and will include a decrease in proliferation of HIV-1-infected cells as well as viral replication. Taken together, these aims will add to our understanding of the mechanisms by which hydrogen peroxide- producing Lactobacillus modulates HIV-1 in the female genital tract, and may add rationale for further evaluation of probiotics as a potential secondary HIV-1 prevention strategy. PUBLIC HEALTH RELEVANCE: The amount of HIV in the vagina and cervix is a major predictor of HIV transmission between sex partners and from mother to child. This study will examine how Lactobacillus, an essential bacteria for vaginal health, works to decrease the amount of HIV in the female reproductive tract.